Date:   Sun, 19 Mar 2023 22:23:36 -0700 (PDT)
From:   Hugh Dickins <hughd@google.com>
To:     Christoph Hellwig <hch@lst.de>
cc:     Andrew Morton <akpm@linux-foundation.org>,
        Matthew Wilcox <willy@infradead.org>,
        Hugh Dickins <hughd@google.com>, linux-afs@lists.infradead.org,
        linux-btrfs@vger.kernel.org, linux-ext4@vger.kernel.org,
        cluster-devel@redhat.com, linux-mm@kvack.org,
        linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-nilfs@vger.kernel.org
Subject: Re: [PATCH 5/7] shmem: open code the page cache lookup in
 shmem_get_folio_gfp
In-Reply-To: <20230307143410.28031-6-hch@lst.de>
Message-ID: <af178ebb-1076-a38c-1dc1-2a37ccce4a3@google.com>
References: <20230307143410.28031-1-hch@lst.de> <20230307143410.28031-6-hch@lst.de>
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Precedence: bulk

On Tue, 7 Mar 2023, Christoph Hellwig wrote:

> Use the very low level filemap_get_entry helper to look up the
> entry in the xarray, and then:
> 
>  - don't bother locking the folio if only doing a userfault notification
>  - open code locking the page and checking for truncation in a related
>    code block
> 
> This will allow to eventually remove the FGP_ENTRY flag.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Acked-by: Hugh Dickins <hughd@google.com>

but Andrew, please fold in this small improvement to its comment:

[PATCH] shmem: open code the page cache lookup in shmem_get_folio_gfp fix

Adjust the new comment line: shmem folio may have been swapped out.

Signed-off-by: Hugh Dickins <hughd@google.com>
---

 mm/shmem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1905,7 +1905,7 @@ static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index,
 	if (folio) {
 		folio_lock(folio);
 
-		/* Has the page been truncated? */
+		/* Has the folio been truncated or swapped out? */
 		if (unlikely(folio->mapping != mapping)) {
 			folio_unlock(folio);
 			folio_put(folio);